It depends exactly how you want to work around this, but if you just need to exclude the null values, then you can override the default ArrayEditor class, something like this;

// define the editor on the property
[Editor(typeof(MyArrayEditor), typeof(UITypeEditor))]
public Test[] test { get; set; }

...

public class MyArrayEditor : ArrayEditor
{
    public MyArrayEditor(Type type) : base(type)
    {
    }

    protected override object[] GetItems(object editValue)
    {
        // filter on the objects you want the array editor to use
        return base.GetItems(editValue).Where(i => i != null).ToArray();
    }
}